Concrete CMS up to 9.5.2 OAuth Callback privileges management

Summaryinfo

A vulnerability was found in Concrete CMS up to 9.5.2. It has been classified as problematic. The affected element is an unknown function of the component OAuth Callback. Performing a manipulation results in privileges management. This vulnerability is cataloged as CVE-2026-81906. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability classified as problematic has been found in Concrete CMS up to 9.5.2. This affects an unknown code block of the component OAuth Callback. The manipulation with an unknown input leads to a privileges management vulnerability. CWE is classifying the issue as CWE-269. The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor. This is going to have an impact on integrity. The summary by CVE is:

Concrete CMS OAuth callback login path prior to version 9.5.3 did not check whether an account was active or email-validated before establishing a session. A deactivated or unvalidated user with an existing OAuth binding could complete authentication and receive a session that was fully authenticated for the callback response, with the login recorded and login events dispatched. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 6.3 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N. Thanks Yonatan Drori from Tenzai for reporting.

The advisory is shared at documentation.concretecms.org. This vulnerability is uniquely identified as CVE-2026-81906 since 08/27/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/11/2026). MITRE ATT&CK project uses the attack technique T1068 for this issue.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Type

• Content Management System

Name

• Concrete CMS

Version

• 9.5.0
• 9.5.1
• 9.5.2

License

• open-source

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